Rotary rock drill



April 4, 1961 D. M. cowAN 2,978,043

' ROTARY ROCK DRILL Filed Dec. 6, 1954 4 Sheets-Sheet 1 r ir MFW flziarzzey.

D. M. COWAN ROTARY ROCK DRILL 4 Sheets-Sheet 4 [720622202 1 flawed? flazmzz.

April 4, 1961 Filed Dec. 6, 1954 In'these drawings? I ROTARY ROCK DRILL David M. Cowan, Columbus, Ohio, assignor to Joy Manufacturing Company, Pittsburgh, Pa., a corporation of Pennsylvania 1 Filed Dec. 6, 1954, 591. No. 473,207 13 Claims. ((11.175-127) This invention relates to rotary drills and more particularly to a rotary rock drill of the high pressure hydraulically operated type wherein-a relatively powerful feeding thrust is applied to the drill bit as the latter is rotated during drilling.

Heretofore, relatively hard rocks or similar materials have been drilled ofttinies by percussive methods due to failure to provide for an adequate feeding thrust on the rotary drill bit and the inadequacy of the drill bit itself.

-With modern tungsten carbide rotary drill bits, it is found possible to apply a tremendous feeding thrust to the'drill bit as a powerful rotative force is imparted to the latter, thus'substantially increasing the drilling etliciency. In such high pressure rotary drills the drill strucing means for imparting powerful feeding forces to the 'drill bit and for anchoring the drill guide frame in a firm position with respect to the work duringthe drilling operation. The drill structure-of the present invention embodies novel features of construction whereby the advantages realized areattained.

Ariobject of the present invention is toprovide an improved rotary rock drillembodying structuralirnprov ements whereby drilling efiiciency is'substantially increased proved rotaryrockdrill of the high pressure hydraulically operated. type wherein a relatively powerful Lfeeding thrust is imparted1 to the drill' bit during drilling. further object is toprovide an improved extendableand col lapsible guiding means'for the elongated drill. steel and drive shaft foriguiding the same atlspaced points along? theirlengths-during the rlr'illing operation Still another object is. toiprovide an improved rotary rock drill having novel combinations andfiarrangements of partsiiThese and other. featuresandadvantages of the invention will,

however, hereinafter more fullylappear;

poses of v illustration one form which the "invention rnay assume in-,pra'ctice. I

Eigfl is-atopplan view of ajr otary drill. constructedinaccordance with a preferred illustrative embodiment of i' the invention. I r Fig. 2"isa side elevational view ofthe drill shown in" Figs;

ht l fi f t i in d-schemes. PP tiOn. 1- I j i In the accompanying drawings ,ther'e'is shownfor purv aiidTBm-takeii together, constitute an- .enlarge d;

- central longitudinal" vertical sectional:viev?- takenon line .3 F 1-; j 'Fig' tis an:enlar dfplan viewof the forward, portion 7 "ofthe drill;partially broken away, and' withfthedrill giformed steel covers. which also add materially "to. the

-tions as the drill operates.

. V I 45 forming'mechanism of the rotary drill. even in hard rock. Anotherob ect is to providecan'irm 2,978,043- Patented Apr. 4, 1961 2 7 Figs. 5 and 5a taken together, constitute an enlarged plan. view of the drill, with parts broken away. i

Fig. 6 is an enlarged cross sectional view taken on line 6-6 of Fig. 3, showing the winding reel for the liquid conducting hose.

Fig. 7 is an enlarged cross sectional view taken on line 7-7 of Fig. 3.;

Fig. 8' is an enlarged cross sectional view taken on line 88 of Fig. 3. Fig. 9 is anenlarged crosssectional view taken on line 9-9 of Fig. 3a.

Fig. 10 is an enlarged cross sectional view taken on line 10-10 of Fig. 3a.

Figs. 11, 12 and 13 are diagrammatic views showing the retracting means associated with the feed chains of the'drill feeding means for progressively. retracting the collapsed drill steel guides.

Fig. 14 is an enlarged perspective view of the forward portion of the drill, showing the multi-pointed stinger bar front end of the guide frame is a work-engaging member 3 desirably in the form of a multi-pointed or serrated- .faced'stinger bar adapted to engage the face of the work, in the manner shown in Figs. 1 and 2. This stinger bar is constantly urged against the work by a power feeding or adjusting device, generally designated 4, for moving the guide frame forwardly along the support-guideways during drilling and this stinger bar serves to steady the guide frame thereby to minimize the setting up of vibra- Guided for back and forth rectilinear movements along the guideways of the guide frarn'e 2 is an actuating means herein desirably a rotating 40 means, generally designated 5, for rotating a drilling impl'ernent or tool 6, the latter desirably'in the form of a conventional hollow rotary drill steel carrying a rotary drill bit 7 of the type knownas a tungsten carbide bit.

Ihjus the actuating 'means 5' constitutes'the work per- In this illustrative construction, the support 1 may be adjustably mounted in various manners and is herein for illustrative purposes shown assupported by a swingable drill bloomson which a supportfi is swiveled about a .tr'ansyerse axis and swivell-y mounted 'on this support :is a-jf'rame Ill turnable about an axis at right angles to the support axis.'- A hydraulic motor 11 serves to turn -*"the'.support about its swivel axis and a hydraulic motor 12' may effect tilting of thesupport 1 about a transverse axis, at 13. By-proper adjustment of the drill boom,the swiveled support and frame, andjthe tiltable guide frame support L the drilling tool r'nay-beadjusted into and held in various drilling positions withirespect to theface of the; Work. 4

in. drilling "to the various guides and mechanisms of-the drill feedyand thisz'housing is provided with properly stren th and sl flness of lhTstructure.

front tubular portion 42 of the bracket 33.

As shown particularly in Figs. 3 and 3a, the drill rotating means 5 serves as an actuating means for the drilling implement and embodies a casing in which a terminal driven shaft 16 is suitably journaled, this shaft arranged with its axis of rotation extending longitudinally of the drill. This shaft has a threaded forward portion 17 to which the drill steel 6 is coupled, as by a coupling member 18. A parallel tubular shaft 19. likewise suitably journaled within the casing, has a spur gear 20 secured thereto which meshes with and drives a spur gear 21 fixed to the shaft 16. Suitably mounted at the rear end of the guide frame 2 is a transmission housing 23 and carried at the rearward portion of this housing is a motor 24, desirably a conventional hydraulic motor, and this housing contains a two-speed transmission or reduction gearing for connecting the motor 24 to an elongated splined drive shaft 25 extending longitudinally of the drill guide frame 2 and journaled on the latter in front and rear bearings 26 and 27. The tubular shaft 19 surounds the shaft 25 and carries conventional splines engaging the splineways of the shaft 25 so that this shaft may drive the intermeshing gearing 20, 21 as the drill rotating means 5 moves rectilinearly along the frame guideways. A motor driven shaft 29 is suitably journaled within the housing 23 and a shiftable clutch member 30 slidingly interlocked with this shaft is manually shiftable by suitable shipper means either to connect a spur gear 31 or a spur gear 32 to the shaft 29. The gear 31 is a low speed gear and meshes with a 'spur gear 33 secured to a shaft 34, likewise suitably journaled within the gear housing and secured to this shaft is a spur pinion 35 meshing with a large spur gear 36 secured to the rearward portion of the splined shaft 25. The gear 32 is a high speed gear and meshes with a spur pinion 35. Thus, depending upon the position of the shiftable clutch member 30, the drill steel 6 may be driven through the reduction gearings at either a relatively low or a relatively high speed.

Mounted at the forward end of the guide frame is a bracket or supporting frame 38 and the face-engaging member or stinger bar 3 is rigidly secured to this bracket. This stinger bar is desirably of tubular sleevelke form, as shown at 39, and closely surrounds the drill steel, as shown most clearly in Figs. 14 and 15. This sleevelike member has a rear flange 40 having openings through which screws 41 extend into threaded connection with a The tubular portion 42 carries a bearing .2 in which the drill steel 6 is journaled. The sleevelike member 39 has itswalls cut away, as by slots 43, to permit ready access to the screw heads and any dirt which may enter the sleeve member may bedischarged laterally through these openmgs.

p The rigid, sleevelike stinger bar 39has a multiplicity of, herein desirably four, equally spaced points OrytOOtl'h like serrations 44 arranged in a circle of small radius from the center line of the drill steel'and these closely spaced points or teeth may bear firmly againstthe working face so that the preloading of the stinger bar is concentric with the thrust load on the brill bit. The stinger bar thus reduces any tendency of relative bending motion between the drill steel and the stinger bar as the thrust load is applied to the drill bit. Thus, the guide frame and drill steel maybe held steady. during axial feeding of the bit.

The power operated means 4 for urging the guide frame forwardly to maintain the stinger bar firmly against the 7 work during drilling comprises a hydraulic motor having ahydraulic cylinder 45 (Fig. 3) secured to and arranged longitudinally within the support 1 and this cylinder contains a reciprocable piston 46 having its piston rod 47 extending forwardly from the front end of the cylinder. This piston rod is threadedly secured at its forward end to ashaft mounting or bracket 48 on the shaft of which a spur pinion 49 is journaled for free rotation. This spur pinion meshes with the teeth of opposed parallel racks 50 and 51respectivelysecuredto the support 1 and the the rotating means 5 along theframe guideways.

slidingly guided in the guideways of theguiding frame and sliding frame 2. Thus, when liquid under pressure is properly supplied to the cylinder 45, the piston is moved within the cylinder to cause the pinion and racks to effect movement of the sliding frame 2 at a speed twice as fast as the rate of travel of the piston 46 thereby to move the stinger bar against the work. A constant leak of liquid under pressure to the rear end of the cylinder causes the piston constantly to urge the stinger bar firmly against the work during the drilling operation.

I ow referring to the feeding means for the drill rotating means 5 for moving the latter rectilinearly back and forth along the guideways of the guide frame 2, it will be noted that a motor 54, desirably a conventional reversible hydraulic motor, is'mounted on the forward portion of the transmission housing 23 (Fig. 3), and the motor power shaft is coupled, at 55, to a horizontal shaft 56 extending longitudinally of the drill and suitably journaled within the gear housing. Secured to the shaft 56 is a worm 57 meshing with a worm wheel 58 having its hub keyed to a transverse shaft 59 suitably journaled within the housing 23. Secured to the shaft 59 is a spur gear 60 (Fig. 2) meshing with a spur gear 61 (Figs. 2 and 7) in turn secured to a parallel shaft 62, the latter likewise suitably journaled within the housing 23. Secured as by keys to the opposite ends of the shaft 62 exteriorly of the gear housing are chain sprockets 63 connected by endless drive chains 64 to chain sprockets 65. The sprockets 65 are secured to aligned transverse shafts 66 suitably journaled within the housing 23 and in turn secured to these shafts are chain sprockets 67 which engage and drive parallel feed chains 68. These feed chains are attached, at their ends, at 69, as shown in Fig. 5, to the sliding drill casing 15 and pass around front guide sprockets 70 journaled on a transverse shaft 71 (Fig. 3a) mounted on an adjustable sliding block 72 in turn mounted in a guideway on a bracket 73 secured to the drill guide frame 2 within the frame 38. This sliding block 72 is adjustable by an adjusting screw 74, to vary the distance apart of the sprockets 70 and 67 to provide for proper tension of the feed chains. The motor 54 has a source of liquid under pressure which is independent of the pressure source for the motor 24. By properly supplying liquid under pressure to the reversible motor 54 the feed chains may be driven to effect feeding of the rotating means 5 either forwardly or rearwardly along the frame guideways.

In order to prevent whipping or lateral vibration of the elongated drill steel 6 as the rotating means 5 moves back and forth along its guideways, there is provided collapsible and extendable guiding means comprising a plurality of, herein desirably three, transverse guide members or steel centralizers 77, 78 and 79 which support bushings 77 in whichthe drill steel rotates. These guides or centralizers have secured thereto lateral guide members 80 which slide in the same guideways as those which guide the rotating means 5 and the guides are pushed forwardly into their collapsed forward position (Fig. 4) by advance of Also located rearwardly of the rotating means 5 is a member 81 and this member 81 and the sliding guide member 78 have depending arms 82 (Fig. 9) which swivelly support guidemembe'rs 83Tand 84 carrying guided bushings 84 which surround and in which guide the intermediate portion of the elongated drive shaft 25 is rotatably supported to prevent undue lateral vibration or whippingrof the latter. It will thus be seen that certain of the sliding guides not only guide the elongated drill steel6 but also serve as guidesfor the elongated drive shaft .25., The parallel feed chains 68 have secured thereto, at diiferent predetermined points along their lengths, lateral projections orside bars 86, 87, 88 and 89 (Figs. 11, 12 and 13) which successively'engage the sliding members or guides to retract or advance the latter as the drill rotating means 5 is moved along the frameguideways. The guides 77, 78 and 79 and the slide member 81 have'openings 91 through which the upper runs of the parallel feed chains 68 pass andthe openings in-theguides 78 and 79 respectively have lateral enlargements 92 and 93 (Figs. 9 and 10) through which the projections or side bars may move and the side bars andopenings in the guides are arranged so that the side bars 86 that engage the rear guide 77 may pass through the opening enlargements 92 and 93 in the front guides 78 and 79. As the drill rotating'means 5 is advanced along the frame guideways from its retracted position, shown in Figs. 3 and 5, the coupling member 18 for the drill steel first pushes against the rear steel guide 77 and as advance of the rotating means 5 continues the steel coupling 18 successively pushes against the steel guides 78 and 79 so that when the rotating means 5 is in its foremost position, shown in'Fig. 4, the three forward guides are collapsed together. .During advance of the drill rotating means the side bars 89 on the feed chains engage the rear guide 81 and move the latter forwardly from the position shown in Fig. 12 to the position shown in Fig. 13, thereby to provide a rear lateral support for the splined drive shaft 25 when the shaft guide 84 is v in its advanced position. During retraction of the drill rotating means from the position shown in Fig. 13 the side bars 86, as the feed chains are actuated, move past the guides 78 and 79 through the enlargements of the openings 91 and engage the rear guide 77 to move the later rearwardly. Thereafter, the side bars 87 move past the frontguide 79 and engage the intermediate guide 78 and finally, the side bars 88 engage the front guide 79 to retract the latter to the desired position, as shown. As the drill rotating means moves rearwardly, its casing engages the rear guide 81 and shoves the latter rearwardly into its retracted position.

In order to supply liquid, desirably water, to the hollow drill steel 6 for flushing cuttings from the hole being drilled in the rock or other material, .a flexible liquid conductor desirably a water hose or conduit 95 is attached, at 96, to the casing of the drill rotating means 5 (Fig. 3). The casing of the rotating means 5 has a waten'chamber 97 with which an axial passage in the shaft 16 com municates and the bore of the hollow drill steel corrimunicates .with the axial shaft passage. To eliminate a troublesome loopof slack hose whenthe drill rotating means moves along the frame guideways, the water hose is wound on a drum 98. As shown inFig. 6, this hose drum is journaled on bearings supported by a transverse shaft 99 supported at its ends within lateral arms 100 secured to thegearhousing 23 on the rear portion of the sliding frame 2. A water supply conduit. 101' is connected, at 102," to one of.the arms 100 and communicatos with a passage 103 in theshaft99, this passage opening laterally out throughone Iside'of the shaft. The pas- Wound on small drums 107-at the'ends of, and coaxial with, the hose drum are wires or cables 108 which exmounted on the brackets 110 securedto'theupper portion of the housing :23 and the forward portions'of these cables extend longitudinallywithin parallel tubes or conduitsf 1:11. secured :to the topof the drill housing 14. Theforward ehcls of these cables are connectedxto elongated coil springs 112 (Figs? 4 and 5a) 'arrangedwithin the-tubes 1111' As the drillrotating means is advanced along the tend forwardly over transverse guiderolls mmmeuy or lugs on'the feed chains. As a result of this-invention, an improved rotary rock drill is provided which is operated under highhydraulio position of the drill rotating means along its guideways. A pair of closely spaced guide sheaves113 (Fig. 5) are journaled on parallel upright axes on the top of the housing 23 and these sheaves serve to guide the water hose 95 as it moves therebetween during movement of the drill rotating means along its guideways.

The general mode of operation of the improved rotary drill is as follows: When the drillis properly positioned on its adjustable mounting with respect to the working face, the hydraulic motor 45 may be operated to actuate the rack and pinion mechanism 49, 50, 51to advance the siiding frame 2 rectilinearly along its. guideways on the support 1 thereby to bring the stinger bar 3 against the face of the work, and this motor acts continuously during the drilling operation constantly to urge the stinger bar firmly against the working face. It may be assumed that the drill rotating means Sis at this time in retracted position on the guide frame and the drill steel rotating motor 24 is running to rotate the drill steel at the proper selected speed under the control of the selective transmission. The feed motor 54 may then be operated to actuate the feed chains 68 to feed the drill rotating means forwardly along the frame guideways thereby to cause the drill bit to penetrate the rock or other mate- .rial being drilled. stinger bar 3 firmly engaging the face close to the drill .bit and the hearing within the bracket portion 42 in which the drill steel is journaled, maintain the bit centered and as the drill rotating means is advanced, the shiftable guides 77, 73,, 79'and 80 serve adequately to support the"intermediate portions of'the elongated drill steel 6 and splined drive shaft 25. p The drillisoperated. at relatively high hydraulic pressures and the force exerted .by the hydraulic frame-adjusting motor 45, which urges the guide frame forwardly against the Working face, may be in the vicinity of 7,000 pounds while the feeding pressures exerted by the feed chains 68 actuated by the feed motor 54 may be in the vicinity of 4,000 to 6,000 pounds. The separate drives for the rotation and feed are provided with independent sources of liquid under pressure so that the demands of one function will not affect the other, thereby to provide greater control over rotation speeds and feed pressures for varying drilling conditions.

As the drill rotating means 5 is advanced to feed the drill bit into the rock or other material, the Water hose 95 wound on the hose drum 98 supplies water through the hollow drill steel to the drill holeto flush away the cuttings and this hose is always maintained under suffi- .cient tension by the coil springs, to avoid undue slack, and the coil springs rotate the drum automatically to .eflectwinding up of the Water hose when the drill' rotating means is retracted Upon reversal of the feed motor 54, the drill rotating means may be, fed rearwardly along the frame guid'eways and the drill steel and drive shaft guides'areautomaticallyretractedby the spaced side bars pressures to effect drilling rapidly and with increased efficiency even in rockwhich is unusually hard. By the provision of the-stinger bar. which engages the working frame guideways-the' water hose 95 by the pullthereon in a direction towind in the cables 108 thereby placing is unwound from thefhosedrum and as the drum 98 rotates in unwinding direction the ,smalldrums 107 rotate.

face at a multiplicity of points close is the center line of .the;drillsteel, the drill is adequately supported and main- :tain ed steady during the drilling operation. The extendable andcollapsible. guides for the elongated drill steel and; drive shaft prevent undue whipping or lateral vibration ofthe parts, thereby to avoid the setting up of excessive vihrationswithinthe machine. By the provision of while undue slackness in the hose is avoided. The rack and pinion mechanism operated by. the adjusting motor the extensible water hose wound on a drum which is automatically rotated as the, drill rotating means moves alongits guideways', water may be supplied to the hollow idrill steel to flush away the cuttings from the hole bottom During starting of the hole the for the guide frame not only firmly urges the guide frame forwardly against the work but also provides for compactness. These and other advantages of the invention will be clearly apparent to those skilled in the art.

While there is in this application specifically described one form which the invention may assumein practice, it will be understood thatthis form of the same is shown for purposes of illustration and that the invention may be modified and embodied in various other forms without departing from its spirit or the scope of the appended claims.

What I claim as new and desire to secure by Letters Patent is:

1. In combination, an elongated guide member providing a longitudinal guideway, work performing n echanism comprising a tool movable back and forth along said guideway, feeding means for said tool including a movable feeding element operatively connected to the tool and means for moving the same to effect feed, said work performing mechanism including a longitudinally extending elongated rotary element, guiding means for supporting and guiding said elongated rotary element at spaced points along its length including separately shiftable guides mounted on said guide member for movement into widely separated guiding positions longitudinally there-along, and means carried and actuated by said feeding element and disposed at spaced points longitudinally along the length thereof for progressively engaging and moving said guides longitudinally of said guide member from adjacent guiding positions as said feeding element moves said tool in'one direction along said guideway.

2. The combination as set forth in claim 1 wherein said guides are guided for movement longitudinally of said guide member in parallelism with said guideway and have openings therethrough which said feeding element extends and moves, and said moving means for said guides comprises elements secured to said feeding element at spaced points therealong and which are engageable with said guides and certain of said guides having openings sufficiently large to enable certain of said moving elements to pass freely therethrough while others of said elements engage certain of said guides to effect movement of the latter therewith.

3. The combination as set forth in claim 1 wherein said rotary element is in the form of a drive shaft and means is provided at the opposite ends of said guide member for journaling said shaft at the ends thereof.

' 4. The combination as set forth in claim 1 wherein said movable feeding element is in the form of a loop and is guided for circulation on said guide member and rotary guiding devices are provided on, said guide member for guiding said feeding element,said moving means for said shiftable guides comprises lugs secured to said feeding element loopat spaced points therealong and arranged progressively to engage said shiftable guides. I

5. The combination as set forth in claim 1 wherein said elongated rotary element is in the form of a drilling implement and said shiftable guides have tubular guiding portions through which saiddrilling implement extends, said guiding portions surrounding said drilling implement.

V 6. In a drill, the combination comprising an elongated I longitudinally extending drill guide frame having a front end located near the working face, an elongated drilling implement and actuating means therefor, said actuating means inciuding an actuating member'movable along said guide frame to move said drilling impiement forwar dly and rearwardly toward and from the work,'a

guide at the front end of said guide frame for guiding said drilling implement, separately shiftable guides disposed rearwardly of the front guide and guided for movement longitudinally alon said guide frame, one of said "rearward guides located forwardly of another and when advanced disposed relatively close together, said rearward guides respectively proyidingbearingsupports and when widely separated engaging the intermediate portion of said drilling implement at points spaced along its length, means for feeding said actuating means along said guide frame comprising a feeding element guided for movement relative to said guide frame and connected to said actuating member, said actuating member as it is advanced. progressively shoving said widely separated rearward guides along said guide frame into closely spaced positions toward said front guide, and means connected to and actuated by said element of said feeding means and secured to said feeding element at spaced points therealong for progressively engaging said rearward guides for progressively moving said rearward guides from their closely spaced forward positions back to their initial Widely spaced retracted positions as said actuating member is moved 'rearwardly alongrsaid guide frame by said feeding element.

7. A drill as set forth in claim 6 wherein said element of said feeding meansconsists of a flexible feeding element guided for circulation on said guide frame and operatively connected to said actuating member, said guide moving means comprising guide-engaging and moving elements secured to said flexible element at predetermined spaced points along its length, said guide-engaging and moving elements progressively engaging said closely spaced rearward guides for retracting the latter as said flexible element is circulated to effect retraction of said actuating means.

8. A combination as set forth in claim 7 wherein said rearward guides have openings through which said flexible element extends, the opening in the front rearward guide being enlarged to permit the guidefengaging element for the rear rearward guide to pass therethrough without interfercnce with the front rearward guide.

9. In combination, a drill guide frame, a drilling implement and actuating means therefor, said actuating means including an actuating member mounted on said guide frame for movement longitudinally therealong to move the drilling implement toward and from the work, driving means for said actuating means comprising a drive shaft extending longitudinally of and journaled on said guide frame, said shaft disposed in parallelism with the path of movement of said actuating member, separately shiftable guides for guiding the intermediate portion of said shaft and movable progressively along said guide frame into widely separated positions as said actuating member is advanced, means for feeding said actuating member along said guide frame, and means connected to and actuated by an element of said feeding means for progressively engaging said guides for shifting said guides along said guide frame into their adjacent retracted positions as said actuating member is retracted.

10. A combination as set forth in claim 9 wherein said drive shaft extends longitudinally forwardly and rear- Wardly with respect to said actuating member and one of said guides is located rearwardly of said actuating member and another is located in advance thereof, said actuating member shoving said front guide forwardly as said actuating member is advanced and said actuating member shoving said rear guide rearwardly as said actuating member is retracted. 1 ll. A. combination as set forth in claim 9 wherein certain of said guides provide a bearing support for the intermediate portion of said drilling implement.

12. In combination, a ide frame, a drilling implement and actuating means therefor, said actuating means comprising an actuating member movable longitudinally diate portions of both said drilling implement and drive shaft.

13. A combination as set forth in claim 12 wherein feeding means is provided for moving said actuating memher along said guide frame and means is connected to and actuated by an element of said feeding means and engaging said guide for shifting said guide along said guide frame.

References Cited in the file of this patent UNITED STATES PATENTS 10 Mitchell July 23, 1935 Mitchell Nov. 5, 1935 Azarowich Jan. 10, 1939 Tilly July 11, 1939 Suzuki Dec. 10, 1940 Curtis Dec. 22, 1942 Dautrebandei. Jan. 8, 1952 Curtis et al. July 7, 1953 Hale Jan. 10, 1956 Hale Apr. 9, 1957 FOREIGN PATENTS France Nov. 18, 1953 

